Progress in understanding the defects in immune regulation which are postulated to exist in human autoimmune diseases has been hampered by our inability to easily identify functional subclasses of human T lymphocytes. The new technique of production of monoclonal antibodies of given specificity from somatic cell hybrids produced by fusion of a selectable mouse plasmacytomia with immune spleen cells offers an excellent tool to produce pure antibodies capable of discriminating between various lymphocyte subtypes. Pioneering work with animal systems has advanced this technique to the point where large numbers of inter or infra species hybrids can be produced, isolated, and maintained in culture. The feasibility of generating clones producing antibody of a desired specificity has been demonstrated. The technique permits isolation of antibodies which are the product of a single cell which recognized a single antigenic characteristic of the immunizing cell surface. Evidence exists suggesting that human lymphocytes, like those of the mouse have surface antigens which correlate with their functional attributes. Thus, it should be possible to produce monoclonal antibodies, analagous to the highly useful mouse alloantisera against Ly antigens that recognize these differences. Rats and/or mice will be immunized whith human T lymphocytes. Their cells will be hybridized with a selectable mouse plasmacytoma. Resulting somatic hybrids will be screened for the production of antibody reacting with lymphocytes. These clones will then be isolated, and the monoclonal antibodies produced tested for specificity for lymphocytes, for their ability to identify a distinct subclass, and to define the function of that subclass in vitro using a variety of tests that will allow assessment of helper, suppressor and effector cell function. When discriminatory antibodies are found they will be grown up in quantity and used to assess the status of that particular regulatory function in patients with autoimmune diseases with emphasis upon systemic lupus erythematosus, rheumatoid artihritis and Hodgkin's disease.